Not understanding of notations in paper: Direct Position-Based Solver for Stiff Rods

[ou-ais]

Thank you for your contribution about position-based simulation of flexible rod.

I am reading the paper "Direct Position-Based Solver for Stiff Rods" and try to implement it by myself. However, there is one equation that I can not understand. I would appreciate it if you could tell me.

The meaning of p and x appearing in the first three rows of Eq. (23) is not understood. Actually, I do not know the difference between p and x.

For p, from the following description of Eq. (23), p1 and p2 is a point on segment 1 and segment 2, respectively, that are given in the local coordinates. Futher, as described in P.5 2nd paragraph, p denotes the position of each segments's center of mass. According to these interpretations, p will be the origin of the local coordinate, i.e. p=(0, 0, 0). Then, the first three rows of Eq. (23) will be x1-x2, is that so?

For x, my understanding is that x is the current position of the center of each segment in world coordinate during Newton iterations, am I right?

Expect your reply.

[janbender]

Sorry for the late reply. x denotes the center of an segment. R is the rotation around the center and p is a connector point on the segment.